Hi all , Will a Scythe Katana 3 fan&heatsink fit into a hp pavilion (a 250n )case ? I googeld it and I found no answers. I just bought a p4 3.2 northwood SL6WG processor and mx-3 thermal compound and 2 gigz .... 4 sticks of corsair 512 mb of ram total of ( 2048 ) of PC3200 (400 MHz) RAM.

I doubt you'll find too many people with first hand experience with a katana and that case. Most people with that case aren't even aware of aftermarket cooling :-) so you're probably better off just measuring. Dimensions of the cooler are above. You'll need 5.63 inched above your CPU surface.